Low-water-loss cement slurry



Patented July 21, 1953 LOW-WATER-LOSS cEMEN'r's URRr Peggy J. Lea, Kansas City, Mo., assignor to Phil lips Petroleum Company, a. corporation of Delaware No Drawing. Application August 29, 1949, Serial No. 113,031

This invention relates to low-water-loss cement slurries. In one aspect, it relates to lowwater-loss cement slurries comprising a hydraulic cement, sufficient water to form a slurry, and

' an eflective amount of a water-loss reducer comprising an alkali lignin sulfonate and an alkali metal salt of an inorganic acid. In another aspect, it relates to low-water-loss cements of the type described, containing a non-cement, inert, granular aggregate material. In still another aspect, it relates to a low-water loss cement slurry containing an efiective amount of a setretarder, such as calcium sulfate and/or calcium chloride.

In the art of cementing oil wells and in groutmodern practice of scratching, or scraping the drilling mud from the wall of the well by mechanical means prior to placing the cement, which often exposes porous formations which will absorb the water from the slurry. This is particularly important when oil sands are penetrated. Artificial contamination of oil sands with Water will often cause shaley impurities in the sand to swell and reduce the permeability of said oil sand to a very great extent. Therefore water lost from the slurry tends to seal off the formation to oil flow. When it is intended to cement with slurry, and then gun perforate the hardened cement, the gun perforator may not be able to penetrate into the region beyond that in which the shaley impurities are swollen by the water extracted from the slurry. In such cases the oil production rate of the well may be severely reduced by water contamination from the slurry.

I have discovered a method for preventing the filtration of water from cement slurries to the absorbent surrounding formations and the resulting contamination of such formations. I do this by adding to the cement slurry a small amount of an alkali lignin sulfonate and a small amount of an alkali metal salt of an inorganic acid, or'an ionizable alkali metalcompound.

One object of the present invention is to provide an improved low-water-loss cementslurry useful for grouting in general, for cementing the walls of wells, and for cementing pipe in wells.

Another object is to provide a low-water-loss cement which will not contaminate the earth formations in bore holes with water to any substantial degree.

2 Claims. (01. 106-90) 6 2 Another object is to provide a cement slurry suitable for use in oil well cementing operations.

Another object is to provide a low-water-loss cement.

Numerous other objects and advantages will be apparent upon reading the accompanying specification and claims.

In preparing the low-water-loss cement slurry, the dry ingredients, comprising hydraulic ce-, ment, with or without additives for increasing the time of set, the inert filler material, such as sandor crushed limestone, and the alkali lignin sulfonate and alkali metal salt may be mixed togetherand later mixed with water alternatively. The water-loss reducers may be mixed separately with hot or cold water, and then added to the (magnesia, for example, may replace part of the lime, and iron oxide a part of the alumina) as are commonly known as hydraulic cements. Hydraulic cements cements, and Portland cements. Puzzolan cements include slag cements made from slaked lime and granulated blast furnaceslag. Because of its superior strength, Portland cement is preferred among the hydraulic cements. In the art, hydraulic cements are recognized as a definite class, and as results of value may be .obtained with any member of that class, it is intended to claim all hydraulic cements. See section 37, page 59, entitled Hydraulic Cementing Materials in General-Introductory from Materials of Construction by Adleburg P. Mills (1915), John Wiley and Sons, New York.

In most oil well cementing andg'routing operations it is generally desirable to use neat cement for added strength but, obviously, it is always possible to add a certain amount of an inert granular filling material or aggregate such as sand, groundlimestone, or any of the other wellknown inert aggregates, as long as the amount added does not reduce the strength-of the cement below the desired value. In operations in open wells it is often desirable to use neat cement, because inert filling material will automatically become detached from the walls of the well,-and

will tend to mix with and dilutetheslurry to such an extent that it is undesirable to add any filling material to the slurry being forced into the well. I

The amount of water added is not critical. It is obvious that sufficient water should be added to form a pumpable slurry, and that when the include. hydraulic limes, grappier cements, puzzolan cements, natural slurry becomes pumpable no further water need be added. One advantage of the low-water-loss slurry of the present invention is that it is not necessary to add excess water over the amount needed for making the slurry pumpable. An additional amount as a reserve for expected losses would tend to reduce the strength of'the cement.

I have found that the addition of a minor amount of an alkali metal, alkaline earth metal, magnesium, or ammonium lignin sulfonate and an alkali metal salt of an inorganic acid to the cement slurry reduces the rate of water-loss from the cement slurry to any water-absorbent medium with which the slurry is in contact. These lignin' sulfonates therefore consist of the alkali metal, the alkaline earth metal, magnesium, and ammonium salts of lignin sulfonic acids. The sodium, potassium, lithium, calcium, strontium, barium, magnesium, and ammonium salts are most en'ective. For economy reasons, the sodium, calcium, and magnesium salts are preferred. Of the alkali metal salts or other compounds which may be added along with the lignin salts, I prefer to use sodium carbonate, sodium hydroxide, sodium sulfate, or sodium oxalate, in the order named.

The structure of lignin is not definitely known. The authorities generally believe that it is a polymer of propyl guaiacol. The lignin molecule is believed to contain at least 1 phenolic hydroxyl group and probably 4 other hydroxyl groups, 3 of which are apparently of equal reactivity and are probably primary alcohol groups. The other, somewhat less group, is probably a secondary alcohol.

Lignin sulfonates are obtained as by-products oi the sulfite process for the production of wood pulp. They comprise a considerable proportion of the original wood and are obtained from the cooking solutions as calcium, sodium, or mixtures of calcium and magnesium salts of lignosulionic acids, depending on the coagulant used.

In the pulping process, it is believed that sulfurous acid is added to an enolic double bond in the lignin molecule. It is believed that lignosulfonic acid is stronger than sulfurous acid and reacts with bisulfite to form the metal lignosulfonate. Emil Ott, in High Polymers, volume V, Cellulose and Cellulose Derivatives, Interscience Publishers, Inc., New York (1946),

on page 487 represents these reactions in Formulas 1 and 2 as follows:

- H on H OH R t=(' r HZSOS R J()-R Llgnin Lignosulfonic Acid H OH hat-R I g Ca(HSOa)z O=S=O Lignosulfonic Acid t 1 11 Ca 211250: 0: :0 J

Calcium Lignosullonate reactive Calcium lignin sulfonate, sodium lignin sul- I'onate, mixed calcium and magnesium lignin sulfonates and basic calcium lignin sulfonates are commercially available from a number of chemical or paper manufacturing companies.

My method is effective in reducing the water loss from any hydraulic cement such as Portland cement or Starcor, which is a hydraulic cement having a retarded set. Starcor differs from Portland cement in that it contains instead of 3CaO.AlzO3, and has a high ratio of di-calcium silicate to tri-calcium silicate, whereas Portland cement has a high ratio of tricalcium silicate to the di-calcium silicate.

My water-loss reducing agents may be mixed with the cement before the ad-zition of water, they may be added to the slurry at the time of mixing, or they may even be added to the water before the mixing of the cement slurry.

Tests were carried out with both Portland cement and Starcor retarded set cement to determine the eifectiveness of my method for reducing the water loss. It will be noted that in some cases, the water loss for a very short period is shown. In those cases where the water loss was complete in less than the usual 30 minute test period, the time for complete water loss is shown along with the amount of filtrate.

In each of the following examples the amount of additive is expressed as the weight per cent based on the amount of dry cement. In each sample, the amount of water is 40% based on the dry cement. This gave a slurry having an approximate density of 15 pounds per gallon. The samples were prepared by adding the required amount of additive and water to a weighed portion of cement. The mixtures were stirred with a spatula for about 30 seconds and then were stirred for about 3 minutes on a laboratory mixer. The following table presents the results of these tests:

Cone. of

. Water loss, Cement Additive additive, ml./min.

as percent '11 s i of cement I Portland None 0 /13 Do Sodium lignin sulfonatc. 1 11/30 Sodium lignin sulionate 1 Do. 5.4/30

\aOH (l. 2 Do. Calcium lignin sullonote" 1 20/02 Calcium lignin sullonate 1 Do 7.3/30

aOH 0. 2 Calcium lignin sulfonate 1 Do. 12/30 Nags O4 O. 2 Calcium lignin suli'onato. 1 Do. 11/30 N82Cz04 0. 2 Calcium lignin sulionetc- 1 Do. 8/30 NazC O3 0. 2 Calcium lignin sulionato. 1 D0. 37/24 NaCl 0.2 Siarcor. None 0 65/02 Do Calcium lignin sulfonate. 1 33/21 Calcium lignin sulfonatc.. 1 Do 11.5/30

N320 O3 (l. 2 l

A portion of each sample was allowed to set to determine the suitability for use in well-cementing and grouting. The treated samples set into hard cement having acceptable physical properties. The blank samples, which had high water losses, set in a cracked and weakened condition. This was, no doubt, the result of incomplete hydration of the cement due to a lack of sufficient water during the setting.

The use of inert filling material in my low-- water-loss cement may be practiced within the scope of my invention.

The foregoing tests have been given for the purpose of illustrating and explaining my invention and it is not intended to limit my invention to the use of the specific mixtures or compositions used in the tests. My invention is defined by the following claims.

Having described my invention, I claim:

1. A cement capable of forming a fluid aqueous slurry when mixed with water consisting of hydraulic cement mixed with from 0.1 to 3 weight per centof a lignin sulfonate selected from the group consisting of alkali metal; alkaline earth metal, magnesium and ammonium lignin sul fonates, and from 0.05 to 3 weight per cent of an ionizable alkali metal compound selected from the group consisting of alkali metal salts of inorganic acids and alkali metal hydroxides, said percentages being percentages of the weight of the dry hydraulic cement.

2. A hydraulic cement aqueous slurry capable of setting in a well, comprising Portland cement, suflicient water to form a pumpable slurry with said cement, and a water loss reducing agent comprising from 0.1 to 3 per cent by weight of the dry cement of a salt of lignin sulphonic acid separated by chemical treatment from other constituents present in waste sulphite liquor and PEGGY J. LEA.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,081,642 Scripture May 25, 1937 2,141,570 Mark Dec. 27, 1938 2,141,571 Kennedy Dec. 2'7, 1938 2,469,353 Alcorn May 10, 1949 2,489,793 Ludwig Nov. 29, 1949 FOREIGN PATENTS Number Country Date 883,027 France 1943 558,563 Great Britain 1944 7 OTHER REFERENCES Emil Ott: High Polymers (1946) p. 456. 

1. A CEMENT CAPABLE OF FORMING A FLUID AQUEOUS SLURRY WHEN MIXED WITH WATER CONSISTING OF HYDRAULIC CEMENT MIXED WITH FROM 0.1 TO 3 WEIGHT PER CENT OF A L IGNIN SULFONATE SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL, ALKALNE EARTH METAL, MAGNESIUM AND AMMONIUM LIGNIN SULIONATES, AND FROM 0.05 TO 3 WEIGHT PER CENT OF AN IONIIZABLE ALKALI METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL SALTS OF INORGANIC ACIDS AND ALKALI METAL HYDORXIDES, SAID PERCENTAGES BEING PERCCENTAGES OF THE WEIGHT OF THE DRY HYDRAULIC CEMENT. 